N-Acetylaspartylglutamate (NAAG) is the most prevalent and widely distributed peptide int he nervous system. NAAG is concentrated in neurons, has been localized in synaptic vesicles and is released by depolarization in a calcium-dependent manner. These and other data support the hypothesis that it is involved in the activation, directly or through glutamate, of acidic amino acid receptors, including the metabotropic "glutamate" receptors. The long term goals of this program remain to define the functional relationship between NAAG and the acidic amino acids, particularly in synaptic communication. Neurons which express high levels of this peptide participate in a very broad spectrum of nervous system functions from sensory-motor to thalamic, hypothalamic, limbic and cortical. The immediate aims involve testing several hypotheses: 1) NAAG functions as a tonic source of receptor activation, directly or through glutamate, thus regulating neuronal excitability; 20 NAAG acts via "metabotropic" glutamate receptors to alter neuronal levels of cAMP, cGMP or calcium and to influence the synaptic release of other neurotransmitters. These hypotheses will be tested in situ via microdialysis to assess the concentration of NAAG in the extracellular space of selected regions of the nervous system and to follow its influence on the release of other transmitters. The metabotropic responses to NAAG will be determined in the isolated chick retina as well as primary cell cultures of cerebellum, cerebral cortex and spinal cord. Additionally, the role of this peptide in discrete physiological systems, which are the focus of other program projects, will be examined in collaboration with members of the program.